Wow, I'm actually delivering on a pledged post within a week. OK, here we go, into the wonderful exciting world of synchronization of electric generators!
Maybe you don't know it, but that juice your electric utility provides you changes direction 60 times a second (assuming you're in the US - Europeans do it slightly differently of course). That's why they call it "alternating current", or AC. There's a diagram on this page with some other stuff too.
Generating electricity that way seems like a lot of trouble, but actually it's easier than producing nonreversing "direct current" (DC). DC requires rectifiers and other impedimenta, and was economically impractical at the time when our electrical distribution network was being built out.
But that alternation creates some problems. For one, it affects the impedance of electrical appliances - vary the rate of alternation and all of a sudden your motorized appliances might overheat. For another, it requires all generators hooked up to feed the system to be exactly in step with the existing rate and amplitude of alternation. That's where synchronization comes in.
They might have better metering stuff nowadays, but many plants synchronize with something called a synchroscope that looks something like a clock with only one hand. The hand rotates at a rate proportional to the difference in speed between the generator being synchronized and the grid it's being synchronized with. The hand position indicates the relative phases of the waves - when it's at 12:00 the waves are exactly in step.
So when you start a prime mover like a diesel generator or a steam turbine, you manipulate its speed with its governor. You set the speed up just a hair higher than that of the grid (as indicated by a slowly moving hand on the synchroscope), let the synchroscope's hand sneak up just short of 12:00, and then you close the breaker to connect it to the grid.
Whoops, you weren't in sync when you closed the breaker? Well, lots of neat stuff can happen then - just don't stand too close. You might fry the windings on your generator. You might jerk your prime mover loose from its mountings, or tear something loose internally. If your generator is big enough relative to the power distribution grid you're supposed to be feeding, you could even bring the whole grid down. That's not a good career move. (And unless you think it's a good idea to redline your car's motor in neutral and then slam it into gear, don't try starting a diesel generator by just connecting it to the grid. That was done at a plant in California back in the 80's, and they managed to break the ~13" crankshaft on a diesel generator).
Well, there's more to it than that yet. You also have to fool with the voltage regulator. This varies current in the exciter to get your generator's voltage at the appropriate value. You want the power to flow out, not in, you want the right power factor (no, not another pledged post!) and you'd better have some reverse power relays ready to knock you offline to protect against idiots and emergencies.
Nowadays more and more of this process is automated. But these functions above still must be carried out in some form or another. And with any luck, if you ever use a backup generator, I hope I've convinced you to read the instructions.
Friday, October 04, 2002
Thursday, October 03, 2002
Where are all the German jokes?
I stole this from Gene Expression (which now features Jason Soon and Suman Palit too - check them out).
Anyway, it got me thinking about German jokes. I don't know any. It's not like there aren't plenty of Krauts around, including me (50%). So where are the jokes?
Anyway, it got me thinking about German jokes. I don't know any. It's not like there aren't plenty of Krauts around, including me (50%). So where are the jokes?
Sillier than a simile
Once in a while I hear an expression that's, uh, memorable. But I daresay I haven't heard them all yet, so I thought I'd try to tap the collective wisdom of The Blogosphere(™ Bill Quick) to see what I've been missing. Here are some examples of the kind of stuff I'm looking for - some of them are, uh, pretty colorful...
For instance, say you want to convey the idea that someone is extremely busy. My two favorite standards are 'a peglegged man in an ass-kicking contest' or 'a one-armed paperhanger with the seven year itch'.
Then there's slipperiness. Most of the ones I've heard are kind of gross. 'Snot on a doorknob' is a worthy entrant, but it can't top this: 'two eels screwing in a bucket of snot'. I about cracked up when I heard that one from an old millwright years ago.
For tightness, there's 'a bull's ass sewn up with a log chain', or 'A gnat's ass stretched over a rainbarrel'.
Confusion? There's 'Father's Day at the trailer park' or '50 blind lesbians at a fish market'.
Human size? I like 'big enough to go bear hunting with a switch'.
Stupidity? 'Too dumb to pour piss out of a boot if the instructions were written on the heel'. I'm thinking the guy who pissed in the boot wasn't so bright either, but maybe some antiquarian can explain the logic to me.
Noisy? 'Like skeletons copulating on a tin roof'. I think I got that from National Review.
I suppose I could go on at great length, as I usually do. But now it's your turn - can you top these?
For instance, say you want to convey the idea that someone is extremely busy. My two favorite standards are 'a peglegged man in an ass-kicking contest' or 'a one-armed paperhanger with the seven year itch'.
Then there's slipperiness. Most of the ones I've heard are kind of gross. 'Snot on a doorknob' is a worthy entrant, but it can't top this: 'two eels screwing in a bucket of snot'. I about cracked up when I heard that one from an old millwright years ago.
For tightness, there's 'a bull's ass sewn up with a log chain', or 'A gnat's ass stretched over a rainbarrel'.
Confusion? There's 'Father's Day at the trailer park' or '50 blind lesbians at a fish market'.
Human size? I like 'big enough to go bear hunting with a switch'.
Stupidity? 'Too dumb to pour piss out of a boot if the instructions were written on the heel'. I'm thinking the guy who pissed in the boot wasn't so bright either, but maybe some antiquarian can explain the logic to me.
Noisy? 'Like skeletons copulating on a tin roof'. I think I got that from National Review.
I suppose I could go on at great length, as I usually do. But now it's your turn - can you top these?
Wednesday, October 02, 2002
Uncivil comments
Let's make a deal, Sgt. Stryker. I won't claim that slavery wasn't involved in the secession of the Southern states in the Civil War, and you won't hand me this sanctimonious crap about how the Union side was fighting to free the slaves and stamp out a culture that was "evil and wicked to the core".
You don't like revisionism? Then what do you think about the fact that the Emancipation Proclamation was written halfway through the war, and didn't free the Northern slaves?
You don't like secession? The general rule is that, unless we're talking about the Mafia, we can leave associations if we choose after we join. Tell me what in the Constitution forbade secession. And if nothing forbade it, tell me why the 10th Amendment doesn't make it legal. The Southerners could see clearly that they were going to get a long brutal screwing once they were no longer in a position to block hostile legislation backed by Northerners, so why should they stick around?
One of the things that amazes me about this topic is how people who ordinarily would make fun of religious fanatics become such sanctimonious pricks themselves when expounding on Northern motives. And in fact a bunch of what could fairly be called religious fanatics provided much of the impetus. They were the abolitionists - a bunch of people who would suffer no economic impact from their radical changes, and who were bound and determined to impose their beliefs on everyone else. There's the analogy to Islamofascism Stryker was looking for - he was just looking on the wrong side.
Yankees have been morally masturbating about their role in ending slavery for a long time now, ignoring the fact that they weren't particularly enlightened about race themselves, and that most of the social disruption would happen far from their neighborhoods anyway. People would lose what historically had been considered property and uneducated ex-slaves would be dumped into the economy with even fewer guarantees than they had had under slavery. Yet back in Boston, where the likes of William Lloyd Garrison did their braying, they wouldn't see any of this. We saw just how tolerant Yankees were, especially Bostonians, over 100 years later, once blacks started migrating north in large numbers.
Slavery certainly doesn't meet modern moral standards, but it wasn't so exceptional by the standards of its time. Should it have been eliminated? Yes. At any price? Don't insult my intelligence - would anyone have voted to prosecute a war knowing it would cost 620,000 dead when many alternatives remained unexplored? Lincoln himself favored shipping blacks back to Africa. And if fighting against it was such a moral imperative, surely it is not diminished now - why aren't we sending troops into the Sudan and other places where the practice survives?
Admit it, the Civil War was about brute force politics and nothing more - the subsequent mythology is the whitewash it takes to cover up the incredible toll. The "save the Union" line sounds like the classic from Vietnam - "we had to destroy the village in order to save it". "With malice toward none"? Right - troops would invade others' property, kill them by the thousands and ruin their economies for years to come, but dammit, we draw the line there. To Stryker, people who have a problem with the way Lincoln, Sherman et al handled the war are "obstinate".
And while Stryker sheds crocodile tears for the slaves, let's note his claimed ties to Philip Sheridan. You remember Sheridan, don't you? He's the alleged source of the expression "the only good Indian is a dead Indian". That's the kind of racially enlightened moral paragons who were leading the armies of the North - after slaughtering their brothers who were defending their homes, what's a few redskins?
You don't like revisionism? Then what do you think about the fact that the Emancipation Proclamation was written halfway through the war, and didn't free the Northern slaves?
You don't like secession? The general rule is that, unless we're talking about the Mafia, we can leave associations if we choose after we join. Tell me what in the Constitution forbade secession. And if nothing forbade it, tell me why the 10th Amendment doesn't make it legal. The Southerners could see clearly that they were going to get a long brutal screwing once they were no longer in a position to block hostile legislation backed by Northerners, so why should they stick around?
One of the things that amazes me about this topic is how people who ordinarily would make fun of religious fanatics become such sanctimonious pricks themselves when expounding on Northern motives. And in fact a bunch of what could fairly be called religious fanatics provided much of the impetus. They were the abolitionists - a bunch of people who would suffer no economic impact from their radical changes, and who were bound and determined to impose their beliefs on everyone else. There's the analogy to Islamofascism Stryker was looking for - he was just looking on the wrong side.
Yankees have been morally masturbating about their role in ending slavery for a long time now, ignoring the fact that they weren't particularly enlightened about race themselves, and that most of the social disruption would happen far from their neighborhoods anyway. People would lose what historically had been considered property and uneducated ex-slaves would be dumped into the economy with even fewer guarantees than they had had under slavery. Yet back in Boston, where the likes of William Lloyd Garrison did their braying, they wouldn't see any of this. We saw just how tolerant Yankees were, especially Bostonians, over 100 years later, once blacks started migrating north in large numbers.
Slavery certainly doesn't meet modern moral standards, but it wasn't so exceptional by the standards of its time. Should it have been eliminated? Yes. At any price? Don't insult my intelligence - would anyone have voted to prosecute a war knowing it would cost 620,000 dead when many alternatives remained unexplored? Lincoln himself favored shipping blacks back to Africa. And if fighting against it was such a moral imperative, surely it is not diminished now - why aren't we sending troops into the Sudan and other places where the practice survives?
Admit it, the Civil War was about brute force politics and nothing more - the subsequent mythology is the whitewash it takes to cover up the incredible toll. The "save the Union" line sounds like the classic from Vietnam - "we had to destroy the village in order to save it". "With malice toward none"? Right - troops would invade others' property, kill them by the thousands and ruin their economies for years to come, but dammit, we draw the line there. To Stryker, people who have a problem with the way Lincoln, Sherman et al handled the war are "obstinate".
And while Stryker sheds crocodile tears for the slaves, let's note his claimed ties to Philip Sheridan. You remember Sheridan, don't you? He's the alleged source of the expression "the only good Indian is a dead Indian". That's the kind of racially enlightened moral paragons who were leading the armies of the North - after slaughtering their brothers who were defending their homes, what's a few redskins?
Coming up to speed
I just got back from Lynne Kiesling's excellent blog, which has a number of good entries related to electric power. Then I remembered that I write about that stuff too. Cool.
Anyway, the post of interest mentioned that it takes time to build more electrical generating capacity. Very true. But even if it's built, you don't get power from a plant immediately. You have to warm it up first.
My observation seems to be that if the temperature is decent, people hop in their cars, start them, and are in gear and moving seconds later. They wouldn't make good power plant operators. Unless you want to risk potentially very costly maintenance problems, you start up slowly.
In particular, steam turbines are touchy about uneven heating. The ones in use at big commercial nuclear power plants are quite large, and the shafts are very long. So long in fact that one of the first things you do when starting up a turbine is to put it on turning gear, so any heat it is exposed to is evenly distributed and you don't make the shaft bow from the weight of all the blades at operating temperature. Even small amounts of bowing of the shaft will cause vibrations which can destroy the turbine.
Piping runs are also very long, and the temperatures in them may vary over several hundred degrees. These factors cause great thermal expansion to occur during startup, accompanied by noises. Heating these pipes too rapidly can cause undue stresses or even failure.
Heat exchangers (see figure 1) like feedwater heaters are also big enough to expand by several inches as they heat up to operating temperatures. The hotter stages will be constructed with one end on wheels to permit the motion required. Meanwhile there are hundreds of interference fits between tubes and the bulkheads they pass through (called 'tube sheets') in these heat exchangers - any of them can leak, lowering the thermal efficiency of the plant.
The part of the plant that produces the steam takes time to warm up too. For nuclear reactors this is further complicated by the need to pull the fuel rods out in special patterns as directed by nuclear engineers to optimize the use of the reactor's power potential. You don't want to do things rapidly with a nuclear reactor unless it's an emergency shutdown (which is called a 'scram').
Once the plant is at operating temperature it becomes more flexible. It can be synchronized to the grid (another post later), and then its load can be varied over a certain range without affecting efficiency and reliability intolerably.
A little consideration of the above tells us something about how electric generation utilities are forced to operate. If they are to be able to pick up loads rapidly and reliably and to accomodate disturbances such as trips, they must always have more generators running than they need to carry the load. And because of the time it takes to heat up, these generators must be running well in advance of the load change. This might force them to run, say, 5 plants at 80% capacity instead of 4 plants at 100% capacity (this of course assumes you have 5 plants of identical capacity using the same fuel, or else there are several other things to consider).
But running 5 plants instead of 4 is expensive - the power to spin the turbine costs money whether it's generating salable electricity or not, and the 4 plant scenario is cheaper than the 5 plant one. So a utility must in a sense act like an insurance company, trying to balance reserves against anticipated demands and still make a profit.
Whoops, I promised another post. Terrific - I can think of about 3 others I've pledged, and one of them is about 2 months old now. The synchronization one will probably come soon though - I'm just getting warmed up.
Anyway, the post of interest mentioned that it takes time to build more electrical generating capacity. Very true. But even if it's built, you don't get power from a plant immediately. You have to warm it up first.
My observation seems to be that if the temperature is decent, people hop in their cars, start them, and are in gear and moving seconds later. They wouldn't make good power plant operators. Unless you want to risk potentially very costly maintenance problems, you start up slowly.
In particular, steam turbines are touchy about uneven heating. The ones in use at big commercial nuclear power plants are quite large, and the shafts are very long. So long in fact that one of the first things you do when starting up a turbine is to put it on turning gear, so any heat it is exposed to is evenly distributed and you don't make the shaft bow from the weight of all the blades at operating temperature. Even small amounts of bowing of the shaft will cause vibrations which can destroy the turbine.
Piping runs are also very long, and the temperatures in them may vary over several hundred degrees. These factors cause great thermal expansion to occur during startup, accompanied by noises. Heating these pipes too rapidly can cause undue stresses or even failure.
Heat exchangers (see figure 1) like feedwater heaters are also big enough to expand by several inches as they heat up to operating temperatures. The hotter stages will be constructed with one end on wheels to permit the motion required. Meanwhile there are hundreds of interference fits between tubes and the bulkheads they pass through (called 'tube sheets') in these heat exchangers - any of them can leak, lowering the thermal efficiency of the plant.
The part of the plant that produces the steam takes time to warm up too. For nuclear reactors this is further complicated by the need to pull the fuel rods out in special patterns as directed by nuclear engineers to optimize the use of the reactor's power potential. You don't want to do things rapidly with a nuclear reactor unless it's an emergency shutdown (which is called a 'scram').
Once the plant is at operating temperature it becomes more flexible. It can be synchronized to the grid (another post later), and then its load can be varied over a certain range without affecting efficiency and reliability intolerably.
A little consideration of the above tells us something about how electric generation utilities are forced to operate. If they are to be able to pick up loads rapidly and reliably and to accomodate disturbances such as trips, they must always have more generators running than they need to carry the load. And because of the time it takes to heat up, these generators must be running well in advance of the load change. This might force them to run, say, 5 plants at 80% capacity instead of 4 plants at 100% capacity (this of course assumes you have 5 plants of identical capacity using the same fuel, or else there are several other things to consider).
But running 5 plants instead of 4 is expensive - the power to spin the turbine costs money whether it's generating salable electricity or not, and the 4 plant scenario is cheaper than the 5 plant one. So a utility must in a sense act like an insurance company, trying to balance reserves against anticipated demands and still make a profit.
Whoops, I promised another post. Terrific - I can think of about 3 others I've pledged, and one of them is about 2 months old now. The synchronization one will probably come soon though - I'm just getting warmed up.
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